Method for removing tiebars after molding of semiconductor chip

ABSTRACT

A method for removing tiebars of a lead frame after one or more semiconductor components have been encapsulated in a resin to form a package body attached to the lead frame, includes preparing a support member and cutters, the support member including holes engageable with the cutters, positioning the lead frame in place on the support member, moving the cutters relative to the support member so that the cutters are fitted into corresponding holes of the support member, punching out tiebars of the lead frame, and thereafter, removing any scraps left between leads of the lead frame.

TECHNICAL FIELD

The present invention relates generally to a process for manufacturing asemiconductor chip package and, in particular, to a semiconductor chippackage using a lead frame having tiebars.

BACKGROUND OF THE INVENTION

FIG. 10A illustrates a conventional packaged semiconductor device havinga resin package body in which one or more semiconductor components areencapsulated and a plurality of leads each connected electrically withthe components and projected outwardly from the package body. In themolding, semiconductor components on a lead frame L of the semiconductordevice are encapsulated with resin to form a package body 2. As shown inFIG. 10B, the leads are connected with the lead frame L and alsoconnected with the neighboring lead or leads 3 through a bridge ortiebar 4 leaving a small gap from a periphery of the package body to bemolded. During the encapsulation process, the tiebars 4 are supposed tofunction as a barrier to minimize an amount of resin leaking out of asmall opening defined between upper and lower mold halves.Disadvantageously, the resin leaked out of the opening and then stoppedby the tiebars 4 form unnecessary residuals or flashing 5 which shouldbe removed afterwards together with the tiebars 4.

For this purpose, a press cutting mechanism is provided on a downstreamside of the molding in the manufacturing process. In general, thecutting mechanism has a die on which the lead frame L is placed. The diehas a plurality of holes defined in a surface adjacent to the packageddevice at respective portions opposing the tiebars 4 and residuals 5when the lead frame L is positioned in place on the die. The cuttingmechanism also has a plurality of press cutters provided above the die.The cutters are designed to move in and out of the corresponding holesso that the tiebars 4 and residuals 5 are cut or punched out into theholes and removed from the package body 2, as shown in FIG. 10C.

With the arrangement, the tiebars 4 and residuals 5 are well removedfrom the package body 2. However, some of the cut portions or scraps canadhere to the cutters after the cutoff operation and, as a result, bebrought back with the cutters moving out of the holes and then clogbetween the neighboring leads 3, which results in an unwantedshort-circuit of the leads 3 and lowers the productivity of the device.

SUMMARY OF THE INVENTION

Hence, it is an object of the present invention to provide an apparatusand method for removing tiebars without leaving any scraps in the leadframe.

It is another object of the present invention to provide a method formanufacturing a semiconductor device capable of removing tiebars withhigh reliability.

To achieve the above object, an apparatus of the present invention forremoving tiebars of a lead frame after one or more semiconductorcomponents have been molded to form a package body attached to the leadframe includes first and second removing stations. The first removingstation includes first and second support members opposed to each othercapable of putting the lead frame therebetween; and a tiebar-cuttingpunch held by the first support member for reciprocation relative to thefirst support member. The tiebar-cutting punch and second support memberhave projections or cutters and holes, respectively, engageable witheach other. In the process, the lead frame is positioned in place, thelead frame is put between the first and second support members, and thenthe cutters are fitted into the corresponding holes in the secondsupport, thereby punching out the tiebars. The second removing stationincludes third and fourth support members opposed to each other capableof putting the lead frame therebetween; and a scrap-removing punch heldby the third support member for reciprocation relative to the thirdsupport member for removing the possible scraps left in between theleads of the lead frame after the tiebars have been removed in the firstremoving station. The scrap-removing punch and fourth support memberhave projections and holes, respectively, engageable with each other. Inthe process, the lead frame is positioned in place, the lead frame isput between the third and fourth support members, and then thescrap-removing punch is moved relative to the fourth support member sothat the projections are fitted into the corresponding holes in thefourth support member, thereby pushing the possible scraps out of thelead frame to the holes.

According to the removing apparatus, after the tiebars (and theresiduals) are removed in the first removing station, the possiblescraps left in between the leads are removed in the second station.Therefore, the tiebars (and the residuals) can be positively removed.

Note that, although according to the present invention the residuals aswell as the tiebars can be removed as described above, reference is notmade hereinafter to the removal of the residuals and the cut portionsthereof for the sake of descriptive simplicity.

A method according to the present invention for removing tiebars of alead frame after one or more semiconductor components have been moldedto form a package body attached to the lead frame includes the steps ofpreparing a support member and cutters, the member being formed withholes engageable with the cutters; positioning the lead frame in placeon the support member; moving the cutters relative to the support memberso that the cutters are fitted into the holes of the support member,thereby punching out the tiebars; and removing the possible scraps leftin between the leads of the lead frame after the moving step.

According to the removing method, after the tiebars are removed, thescraps that may be left in between the leads are removed. Therefore, thetiebars can be positively removed.

A method according to the present invention for manufacturing asemiconductor device includes the steps of molding one or moresemiconductor components positioned on a lead frame to form a packagebody; removing remaining gates after the semiconductor components havebeen molded; and removing tiebars after the remaining gates have beenremoved. The step of removing the tiebars includes the steps ofpositioning the lead frame in place on a support member formed withholes; moving cutters relative to the support member so that the cuttersare fitted into the corresponding holes of the support member, therebypunching out the tiebars; and removing the possible scraps left inbetween the leads of the lead frame after the moving step.

According to the manufacturing method in which the “remaining gates” areremoved before the removing process of the tiebars, components in thefirst and/or second removing station are prevented from being damagedbecause of the remaining gates during the removing process of thetiebars and/or scraps. Therefore, a high reliable removing operation ofthe tiebars can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the tiebar-removing device according tothe present invention;

FIG. 2 is a cross sectional view of a first removing station, takenalong line the II-II in FIG. 1, which is perpendicular to a guidingdirection of a lead frame;

FIG. 3 is a cross sectional view of a second removing station, takenalong the line III-III in FIG. 1, which is perpendicular to a guidingdirection of a lead frame;

FIG. 4A is an enlarged cross sectional view of punching projections ofthe second removing station;

FIG. 4B is an enlarged cross sectional view of a variant of punchingprojections of the second removing station;

FIG. 5 is a schematic diagram showing projections of a tiebar-cuttingpunch, fitted into corresponding through holes of a die in the firstremoving station;

FIG. 6 is a cross sectional view of another die in the first removingstation;

FIG. 7 is a cross sectional view of a mechanism for detecting thedetachment of the lead frame;

FIG. 8 is a cross sectional view of a mechanism for removing resinsremaining at the gate;

FIG. 9A is a partial cross sectional view of the mechanism in FIG. 8 inthe process of cutting the remaining resins;

FIG. 9B is a partial cross sectional view of the mechanism in FIG. 8,which has just cut the remaining resins;

FIG. 10A is a side view of a semiconductor device having a resin moldedchip;

FIG. 10B is a top view of a portion of a typical lead frame having atiebar structure; and

FIG. 10C is a top view of a tiebarless lead frame.

Corresponding reference numbers indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows schematically an embodiment of a tiebar-removing deviceaccording to the present invention. The device has a first removingstation 6 for removing tiebars after a molding process and a secondremoving station 7 downstream of the station 6 with respect to theguiding direction of the lead frame for removing scraps that may be leftin between leads after the first removing station 6 has removed thetiebars.

Referring to FIG. 2, the first removing station 6 includes a lower dieset 8, to which guide posts 9 extending in the vertical direction arefixed. An upper die set 10 is supported on the guide posts 9 forvertical movement relative to and along the guide posts 9.

A die plate 12 is fixed on the lower die set 8. A tiebar-cutting die 16is removably mounted through a spacer 14 on the die plate 12. The die 16constitutes a lower supporting member (second supporting member) which,in combination with an upper supporting member described below, servesto engage a lead frame L therebetween during the cutting process of thetiebars. In order that, where the die 16 is abraded to some extent, itis detached and polished to reuse, the spacer 14 is replaced with a newone which is thicker by the thickness of the polished portion of the die16 to adjust the height of the top surface of the die 16. The die 16 hasa plurality of through holes 16 a in the upper portion which, incombination with a plurality of projections of the tiebar-cutting punchdescribed below, serve to punch out or cut the tiebars. The hole pitchis equal to the lead pitch of the lead frame L. The through holes 16 aare connected with a scrap-exhausting hole 16 b formed in the lowerportion of the die 16. In order to discard the cut portions or scraps ofthe tiebars from the device, scrap-exhausting holes 8 a, 12 a and 14 aare formed in the lower die set 8, the die plate 12 and the spacer 14connected with the scrap-exhausting hole 16 b.

A backing plate 18 is fixed on the lower surface of the upper die set10. On the lower surface of the backing plate 18 is fixed a punch plate20, on which guide posts 24 extending in the vertical direction arefixed for supporting a stripper plate 22 for vertical movement. On thestripper plate 22 is fixed a stripper piece 28, on the lower surface ofwhich pilot pins 26 are mounted in place. The stripper piece 28constitutes an upper supporting member (first supporting member) which,in combination with the lower supporting member, serves to engage thelead frame L therebetween during the cutting process of the tiebars.

On the upper surface of the stripper plate 22 are fixed one ends of pushrods 30, which are extended in the vertical direction through thebacking plate 18 and punch plate 20. The other ends of the push rods 30are connected with respective coil springs 32 provided within the upperdie set 10 for biasing the push rods 30 downwardly. In the drawing,reference number 34 indicates a bolt for incorporating the respectivecoil spring 32 in the upper die set 10.

The first removing station 6 includes a tiebar-cutting punch 36. Thepunch 36 has a plurality of projections or cutters 36 a which, incombination with the through holes 16 a of the die 16, serve to, punchout the tiebars. For this purpose, the size and pitch of the projections36 a are designed so that they are capable of being fitted into thecorresponding through holes 16 a of the die 16.

The punch plate 20 is formed with an opening for incorporating thereinand holding the upper part of the tiebar-cutting punch 36. A spacer 38is provided between the upper end of the punch 36 and the backing plate18. In order that, where the punch 36 is abraded to some extent, it isdetached and polished to reuse, the spacer 38 is replaced with a new onewhich is thicker by the thickness of the polished portion of the punch36 to adjust the height of the lowermost surface of the punch 36. Thepunch 36 is removably attached to the punch plate 20 by means of punchholders 42, each of which is fastened by a bolt 42.

The stripper piece 28 is provided with a plurality of guides 28 a thatare fitted in the respective recesses between the adjacent projections36 a of the punch 36. The guides 28 a are designed with a high degree ofgeometrical accuracy so that they can guide the projections 36 a of thepunch 36 without rocking in the transverse direction when the punch 36is moved in the vertical direction relative to the stripper piece 28 aswill be described hereinafter.

A pair of opposing guide rails 44 is provided between the die 16 andstripper piece 28 for guiding the lead frame L from a molding device(not shown) to the first removing station 6 and then to the secondremoving station 7. The guide rails 44 have a plurality of through holes44 a for receiving the pilot pins 28 of the stripper piece 28 toposition the lead frame L relative to the stripper piece 28. The guiderails 44 are designed so that it can be moved in the vertical directionbetween a home position shown where they are located between and spacedfrom the die 16 and stripper piece 28 and a tiebar-removing positionwhere they are sandwiched between the die 16 and stripper piece 28. Asdescribed below, the downward movement of the stripper piece 28 allowsthe guide rails 44 to be pressed by the stripper piece and movedownwardly to the tiebar-removing position.

Referring to FIG. 3, the second removing station 7 is similar to thefirst removing station 6 except for the details described hereinafter.Specifically, the second removing station 7 includes a scrap-removingpunch 136 with projections 136 a that are capable of fitting intocorresponding through holes 116 a of a die 116 to push out the scrapsthat may clog between the leads and drop them to a scrap-exhausting hole116 b formed in the die 116. The stripper piece 128 and die 116constitute an upper or third supporting member and a lower or fourthsupporting member, respectively, to put the lead frame L therebetweenduring the removing process of the scraps.

It should be noted that the projections 136 a of the second removingstation 7 need not function as cutters, unlike the first removingstation 6. Each of the projections 136 a may have a cross sectionidentical to that of the projection 36 a in the first removing station 7(and thus the tiebar portion to be cut by each projection 36 a).However, each of the projections 136 a may be designed so that it has across section smaller than that of the projection 36 a in the firstremoving station 7 (and thus the tiebar portion to be cut by eachprojection 36 a) as shown in FIG. 4A, as long as the cross section ofthe projection 136 a is large enough to push out the scraps T caught inbetween the leads. Preferably, as shown in FIG. 4B, the projections 136a may be tapered in the downward direction to improve the strengththereof. In addition, the punch 136 (or at least the projections 136 athereof) may be formed with resin, so that the lead frame L is preventedfrom being damaged in case where the lead frame L and projections 136 amay interfere with each other during the removing process of the scrapsT.

The punch 36 of the first removing station 6 is aligned and guided withhigh accuracy by the guides 28 a of the stripper piece 28 that arefitted in between the corresponding adjacent projections 36 a of thepunch 36. On the other hand, the punch 136 of the second removingstation 7 can remove the scraps that may be left in between the leadseven if the alignment accuracy of the projections 136 a is lower thanthat of the projections 36 a. Therefore, guiding portions such as theguides 28 a may be omitted in the stripper piece 128 and only theperiphery of the punch 136 may be guided by the stripper piece 128, asshown in FIG. 3. This result in the constructional simplicity of thestripper piece 128, providing a tiebar-removing device at lower cost.

The operation of the tiebar-removing device will now be described.Referring to FIG. 2, the lead frame L is guided along the guide rails 44and transported to the region above the die 16 of the first removingstation 6. Next, the upper die set 10 is moved downwardly in thevertical direction along the guide posts 9. Accordingly, the stripperplate 22 and stripper piece 28 fixed thereto are moved downwardly in thevertical direction along the guide posts 24, so that the pilot pins 26on the lower surface of the stripper piece 28 are inserted through theholes 44 a of the guide rails 44 into corresponding locating holes notshown in the lead frame L. As the lead frame is positioned relative tothe stripper piece 28, the stripper piece 28 presses the guide rails 44downwardly.

The further downward movement of the upper die set 10 brings thestripper piece 28 in touch with the die 16 to press the lead frame Ltoward the die 16. With the additional downward movement of the upperdie set 10, the stripper piece 28 presses the compressed coil springs 32via the respective push rods 30, which in turn increases the reactionforce to compress the lead frame L toward the die 16. The punch 36 isalso moved downwardly along the guides 28 a of the stripper piece 28 sothat the through holes 16 a of the die 16 and the correspondingprojections 36 a of the tiebar-cutting punch 36 engage with each otherto punch out the tiebars. FIG. 5 shows the fit of the projections 36 aof the punch 36 into the corresponding through holes 16 a of the die 16.The tiebars that have been cut are discarded through the exhaustingholes 16 b, 14 a, 12 a and 6 a in this order out of the removing device.

Then, the upper die set 10 is moved upwardly to permit components of thefirst removing station 6 to operate reversely so that the guide rails 44are returned to their home position. Note that when the punch 36 ismoved upwardly to return to its original position, the stripper piece 28prevents the lead frame L from moving upwardly together with the punch36.

As described above, when the projections or cutters 36 a of the punch 36in the first removing station 6 are pulled out of the holes 16 a of thedie 16, the portions that have been cut may be lifted and caught inbetween the neighboring leads of the lead frame L. According to thepresent invention, for removal of such cut portions or scraps, the leadframe L is transported along the guide rails 44 to the second removingstation 7.

The transported lead frame L is held in the second removing station 7 sothat the regions in the lead frame L where the tiebars have been cut areright above the through holes 116 a of the die 116 (see FIG. 4A). Then,components in the second removing station 7 are operated in thesubstantially same way as the corresponding components in the firstremoving station 6. Specifically, the projections 136 a of the punch 136are fitted into the through holes 116 a of the die 116 to push out thepossible scraps caught in between the leads so that they are discardedthrough the exhausting holes 116 b, 14 a, 12 a and 4 a in this order outof the removing device.

According to this embodiment of the tiebar-removing device, the scrapscaught in between the leads in the tiebar removing process in the firstremoving station 6 are completely removed in the second removing station7, which allows the yield of a semiconductor device to be improved.

Since the present invention has been described by way of the exampleswith reference to the accompanying drawings, it is to be noted thatvarious changes and modifications will be effected without departingfrom the spirit and scope of the present invention.

For example, as shown in FIG. 6, the exhausting holes 216 b in the die216 of the first removing station 6 may be connected with one or morevent holes 217 for supplying gas (e.g. air) to the projections orcutters of the punch when they are fitted in the holes of the die 216.This restrains the scraps attached on the tips of the projections frombeing lifted when the projections of the punch are pulled out of theholes of the die 216.

Also, a mechanism for detecting the detachment of the lead frame L fromthe guide rails may be provided in the removing device in order toprevent the lead frame and/or components of the removing stations frombeing damaged in the tiebar- and/or scrap-removing operation. Anexemplary detecting mechanism is shown in FIG. 7 in which a pair ofopposing guide rails 344, which is formed with grooves 345 along whichthe lead frame L is guided, has openings 347 positioned above and belowthe corresponding grooves 345. Sensors 343 (e.g. photo sensors such aslight emitters and receivers) are provided externally of the openings345 so-that they can detect the detachment of the lead frame L from thegrooves 345.

As known in the art, resins may remain at the gate (which is hereinreferred to as “remaining gates”) after the lead frame has been moldedto form a package body. Therefore, when the tiebars are removed in thefirst removing station 6 with the resins remaining at the gate, they maydamage components such as die. Accordingly, it is preferable to trim offthe remaining gates before the cutting process of the tiebars in thefirst removing station 6.

FIG. 8 shows a partial cross sectional view of a gate cutting station.The station 50 has a configuration similar to that of the first removingstation 6. In FIG. 8, the similar elements are indicated by referencenumbers with a hundreds digit of 4. The gate cutting station 50 isconfigured so that it cooperates with the first and second removingstations 6 and 7. Specifically, the gate cutting, first removing andsecond removing stations 50, 6 and 7 are positioned in this order withrespect to the guiding direction of the lead frame L, which is in theform of a ribbon and guided along the guide rails 44. The downwardmovement of the upper die set 10, which is a common element to the gatecutting, first removing and second removing stations 50, 6 and 7, allowsthe gate-, tiebar- and scrap-removing process to be simultaneouslyperformed for respective lead frame portions positioned in place in thestations 50, 6 and 7, respectively.

The station 50 has a lifter 52 with a projection 52 a opposed to theremaining gates G of the lead frame L. The lifter 52 is connected at itsone end with a coil spring 54, which is provided within a hole formed inthe lower die set 408, die plate 412 and die 416 for biasing the lifter52 upwardly. In the drawing, reference number 56 indicates a bolt forincorporating the coil spring 54 in the hole.

The stripper piece 428 has a projection 428 b opposed to the projections52 a of the lifter 52 so that the lead frame L transported along theguide rails 44 is interposed therebetween. The projection 52 a serves tosupport the surface opposite the surface with the remaining gates Gthereon when the stripper piece 428 is moved downwardly. By the furtherdownward movement of the stripper piece 428, the projection 428 bcooperates with the projection 52 a of the lifter 52 to trim theremaining gates.

A press pin 58 is fixed to the plate 420. The press pin 58 is fitted forvertical movement in the through hole formed in the stripper plate 422and stripper piece 428. The upper surface 52 b of the lifter 52 isopposed to the lower surface 58 a of the press pin 58 to make contactwith the press pin 58 when the press pin 58 moves downwardly. In orderto simplify an understanding of the construction, the press pin 58 isshown as if it is provided for downward movement across the lead frame Ltoward the lifter 52 in the drawing. However, the press pin 58 isdesigned so that it does not interfere with the lead frame L during itsdownward movement.

The lowermost surface 422 a of the stripper plate 422 is set to have thesubstantially same height as that of the lower surface 428 a of thestripper piece 428. The uppermost surface 412 a of the die plate 412 isset to have the substantially same height as that of the tip of theprojection 52 a of the lifter 52 in its top position biased by thespring 54.

With the gate cutting station 50 so constructed, the lead frame L istransported along the guide rails 44 to the region above the die 416 inthe gate cutting station 50. Next, the upper die set (not shown) ismoved downwardly in the vertical direction along the guide posts (notshown). Accordingly, the stripper plate 426 and stripper piece 428 fixedthereto are moved downwardly in the vertical direction along the guideposts (not shown), so that the pilot pins 426 on the lower surface ofthe stripper piece 428 are inserted through the holes (not shown) of theguide rails 44 into corresponding locating holes (not shown) in the leadframe L. Thus, the lead frame L is brought in alignment with thestripper piece 428. Then, as shown in FIG. 9A, the die plate 412 blocksthe movement of the stripper plate 422 while the projections 428 b and52 a of the stripper piece 428 and lifter 52, respectively, trim off theremaining gates. At this moment, the tiebar/scrap-removing process isnot performed in the removing stations 6 and 7.

The further downward movement of the upper die set and the plate 420fixed thereto allows the press pin 58 to be guided downwardly in thethrough hole formed in the stripper plate 422 and stripper piece 420.Then, as shown in FIG. 9B, the press pin 58 is brought in touch with thelifter 52, so that the lifter 52 is pushed downwardly against a biasingforce provided by the spring 54 to space the projection 52 a of thelifter 52 from the lead frame L.

With the projection 52 a of the lifter 52 spaced away from the leadframe L to the extent that the projection 52 a does not make contactwith the lead frame L, the tiebar/scrap-removing process is performedfor the lead frame portions in the first and second removing stations 6and 7. Use of such gate cutting mechanism for vertical movement allowsthe remaining gate, tiebar and scrap removing processes to be performedwith high reliability and efficiency.

According to the present invention, it is ensured in the manufacturingof a semiconductor that the tiebars are completely removed after themolding process, which result in an improved yield of the semiconductor.

1-4. (canceled)
 5. A method for removing tiebars of a lead frame afterone or more semiconductor components have been encapsulated in a resinto form a package body attached to the lead frame, comprising: preparinga support member and cutters, the support member including holesengageable with the cutters; positioning the lead frame in place on thesupport member; moving the cutters relative to the support member sothat the cutters are fitted into corresponding holes of the supportmember, punching out tiebars of the lead frame; and thereafter, removingany scraps left between leads of the lead frame.
 6. The removing methodin accordance with claim 5, wherein removing any scraps comprises:preparing a second support member and projections, the second supportmember including holes engageable with the projections; positioning thelead frame in place on the second support member; and moving theprojections relative to the second support member so that theprojections are fitted into the corresponding holes in the secondsupport member, pushing the scraps out of the lead frame and into theholes.
 7. The removing method in accordance with claim 5, wherein movingcomprises supplying gas to the cutters of the first punch when thecutters are fitted into the corresponding holes of the support member.8. A method for manufacturing a semiconductor device, comprising:encapsulating at least one semiconductor component positioned on a leadframe in a resin to form a package body; removing remaining gates afterthe semiconductor component has been encapsulated; and removing tiebarsof the lead frame after the remaining gates have been removed, whereinremoving the tiebars comprises positioning the lead frame in place on asupport member including holes; moving cutters relative to the supportmember so that the cutters are fitted into corresponding holes of thesupport member, punching out the tiebars; and thereafter, removing anyscraps lefts between leads of the lead frame.